Here is the full list of all 15 Riddles of the Owls Kingdom achievements.
All levels with 3 stars
All Trophies collected
"Vast Step" world complete
Fully restored owl's house
"Immense Taiga" world complete
100 levels with 3 stars
Hints used in 3 levels in a row
Collect all owls in their house
"Unassailable Mountains" world complete
60 levels with 3 stars
40 levels with 3 stars
"Endless Sands" world complete
20 levels with 3 stars
Solved level in less, then 120 seconds
Tutorial finished